I dont think there is a difference in usage for "zahlen" and "bezahlen".
The only thing that comes to mind is that in some serious scenarios (for example buying a new car) you would be more likely to hear "bezahlen" because it is slightly more polite.
I for example use "zahlen" more often because I speak rather fast; it is faster to say instead of "bezahlen" .
The translation I have is . I had assumed that would translate as because it's a declined article and that is probably a valid translation. My query is whether should be declined when it's being used as a number (ein, zwei, drei) or whether I am overthinking this. I suspect is just the declined article and is the given translation as it sounds more natural in English. But just in case I am missing something about numbers ...